The Ubaidians may have introduced the Sumerians to the rudiments of writing and numerical calculation, which the Sumerians used for calculating and to keep records of supplies and goods exchanged.
The Sumerians wrote arithmetic based on units of ten – the number of fingers on both hands.
Sumerian priests had once worked the fields alongside others, but now they were separated from commoners.
A corporation run by priests became the greatest landowners among the Sumerians.
The priests hired the poor to work their land and claimed that land was really owned by the gods.
Priests had become skilled as scribes, and in some cities they sat with the city's council of elders.
By 3800 BCE the Sumerians had supplanted the Ubaidians and Semites in southern Mesopotamia.
They built better canals for irrigating crops and for transporting crops by boat to village centers.
They built seaworthy ships, and they imported from afar items made from the wood, stone, tin and copper not found nearby. Some people were more wealthy than others, and political power was unevenly distributed.Presumably before the time of the Sumerians, kings were chosen by the warriors, with the king as the leading warrior.Kings are described as working in conjunction with the priesthood.In the center of each city was a temple that housed the city's gods, and around each city were fields of grain, orchards of date palms, and land for herding.According to Samuel Noah Kramer, early in Sumerian civilization a temple corporation owned "some of the land, which it rented to sharecroppers; the remainder was the private property of individual citizens.